The present invention relates to a stable organic liquid dispersed copolymer of the vinyl series formed from a plurality of components having various polarities, and to a method of making the same.
The present invention is especially suitable for preparing a stable organic liquid dispersed liquid of a polymer containing a hardening functional group in the molecule.
It is known to prepare a stable dispersed liquid of a vinyl polymer by polymerizing the vinyl monomer in an organic liquid, thereby forming dispersed particles of the vinyl polymer which are insoluble in said organic liquid, characterized by polymerizing in the presence of a compound containing a component which is to be solvated by the organic liquid, and a vinyl group copolymerizable with said monomer. This procedure has been proposed in Japanese patent application publication No. 19186/1965.
In such process, when two or more vinyl monomers which are remarkably different in polarity are copolymerized, it is recognized that the composition and its characteristic values such as degree of polymerization of the resulting copolymer, vary remarkably in respect of ratio of polymerization. They accordingly become non-uniform, which is undesirable for many practical purposes. This is perhaps because the polymerization rate and the copolymerization reaction ratio differ with the size or difference of polarity between the respective monomers and the organic liquid.
For improving upon this irregularity, a process has been proposed which comprises adding a monomer having high polarity to the reaction system during the polymerization reaction (Japanese patent application publication No. 20303/1968).
However, uniformity of composition is especially required when producing a copolymer from a multi-component (in many cases 4- or 6-component) monomer, wherein the respective components differ remarkably in polarity such as, for example, producing a thermosetting copolymer, or for producing low molecular weight copolymers such as for paints, for example. Therefore, the process of Japanese patent application publication No. 20303/1968 cannot be called an effective process for the purpose. In a polymer dispersed liquid, especially when a thermosetting polymer is used, the speed or degree of setting tends to become a problem. Specifically, when the thermosetting polymer uses a cross-linking agent such as, for example, an alkylated amino resin, setting is unlikely to proceed sufficiently unless these cross-linking agents are completely contained in the polymer particles. This is perhaps due to the fact that cross-linking takes place only locally. Accordingly, various special expedients have been used for the preparation of a polymer dispersed liquid using a cross-linking agent.
For example, a process has been proposed for preparing a polymer dispersed liquid which comprises dissolving an alkylated amino resin in a non-aqueous solvent, adding to the resulting solution a first active ethene monomer and a second active ethene monomer each having a functional epoxy group, respectively and copolymerizing both of these ethene monomers (however, not containing a functional hydroxyl group, respectively) in the presence of an alkylated amino resin (Japanese published patent applications Nos. 8537/1972 and 11838/1972).
Further, a process has been proposed for preparing a polymer dispersed liquid which comprises reacting a pre-reaction agent having a group which can be condensed with a melamine-formaldehyde resin and a double bond copolymerizable with a melamine-formaldehyde resin, with a melamineformaldehyde resin thereby preparing a copolymerizable alkylated melamine-formaldehyde resin reaction product functioning as a dispersion stabilizer precursor, and polymerizing a vinyl monomer which does not contain hydroxyl or carboxyl functional groups in an organic liquid dissolving this stabilizer precusor (Japanese published patent application No. 11397/1972).
However, in each of the aforesaid processes it is indispensable that the melamine-formaldehyde resin or reaction product thereof must dissolve in the solvent. On the other hand, it is indispensable that the polymer be insoluble in the solvent. Accordingly, the melamine-formaldehyde resin or reaction product thereof is not likely to be included sufficiently in the polymer particles. Further, because carboxyl groups are not present in the polymer particles, acceleration is not likely to occur in the cross-linking reaction.
Japanese patent Application publication No. 21581/1972 relates to a process for preparing a stable polymer dispersed liquid, which process comprises copolymerizing vinyl monomers consisting of alkyl acrylates, alkyl methacrylates, styrene, acrylonitrile and an acryl amide which does not contain any --OH or --COOH functional groups, in the presence of a liquid obtained by dissolving an alkylated melamine-formaldehyde reaction product in an aliphatic hydrocarbon, with an acrylic acid monomer or methacrylic acid monomer having an --OH and/or --COOH functional group. However, in this case also, the copolymer is insoluble in the solvent, because a substance is used which is soluble in the aliphatic hydrocarbon. The melamine-formaldehyde reaction product is not likely to be included in the polymer particles.
The present invention overcomes the foregoing disadvantages, providing a stable dispersed liquid of a copolymer having a uniform composition.